Tom. M

Time for some rennlist idea hunting.

Car is a 82 body with 91 S4 engine and brains. Using 82 fuse panel.

Everything seems to have been swapped in fairly nicely. Had issues with 4 cylinder running that was cured by a coil swap.

Runs good for short periods of time including driving 60 plus miles for alignment. Seems to progressively run worse after each start..morning start..fine....stop for gas..seems to begin stumbling, stop for coffee...running really bad..finally not able to drive down the street bogging down bucking etc. It almost feels like I can coax it to rev but it's delicate..almost as if too much fuel. It does smell rich.

Seems if I let it sit overnight or longer with battery disconnected it will go back to running OK..until the next startup (after hot). Disconnected the MAF but no significant change in running condition.

Case in point: Ran up to the shop yesterday (about 30 miles)...car started OK after sitting for a week or so. Get to the shop no probs..move car around OK...after about the third start..starts to surge and then won't hold idle..not quite dying but not able to rev...backfiring in exhaust. Get ready to leave seems to start OK..as I get down the road starts to buck and kick..rich smell, get her towed back to the shop..and catch a ride home..

Wires are bad (firefly's at night) but I don't think it's bad enough to cause this.
Output stages up front have been swapped with known good unit..no change.

I'm going to bring my GT brains and maf and swap those in just to see if it runs differently.

I'm looking for any and all suggestions for things to test or swap out.

Also want to add that the ign monitoring relay has the bypass relay in there.

PorKen

Did you try swapping mechanics?



Correct (LH) Temp II? Low resistance (100-300ish ohms) from each terminal to ground when warm?

Tom. M

Well..don't think Thurston would take too kindly to getting let go haha...I save my electrical troubleshooting for him...give me mechanical..no probs...give me intermittent electrical (or sensor) issues..and you'll hear me make up some new swear words..

I'll probably have to attack it from that route..check every sensor..temp I, II, throttle position switch, O2 sensor etc...

Is there a way to test the output stages up front?

atb

When I was reading your symptoms Tom, this was the first thing that came to mind. I'd swap out the wires. It may be easiest just to leave them connected to the distributor caps, and swap out the caps w/ wires with the set on your GT. I've also got set of wires up at the shop.

Tom. M

Car's at the shop right now..Thanks to JT for getting me home last night... Found the wires from your 87 motor...but those looked as bad or worse than the ones on there (from my GT when I swapped to the magnecors). It still doesn't make sense that the running would get worse after each start though..maybe the wires get warm..making the cracks worse?

Skiviking

That would be the "first" thing to correct is the wires....you'll spend and waste more time trying to track down your problem until you eliminate this sure problem. Just an observation....best of luck on the fix...

Jim M.

I've known coils to fail as they get hot. Another thought, do you have a cat on the car? Could it/they be plugged up? The "smells rich" clue should give you a starting point. Does it run well when cold without disconnecting the battery between failures?

Tom. M

....:lurk mode on...hiding from epa regulators: custom X-pipe with dual pipes all the way back...so no cats... :lurk mode off: ..

I haven't left the battery connected for extended periods..just out of force of habit. When I head back to the shop, I'll reconnect..(put on a trickle charger) and leave it like that..to see if it makes a diff. I too suspect the coil, but though that it was either ..good .....or bad?.... Gonna trade that drivers side out too (other one has been swapped already..known to be bad) and see if it makes a difference.

heinrich

check ignition, replace plug wires and if it persists, check 2nd stages

atb

Tom, I've got a set of Magnecors for the stroker, they should be around there somewhere. (Maybe with your steering column bolts. )
Heat raises the resistance of the wires doesn't it? Maybe as the engine (and wires) get hot, the resistance in the wire gets too high and the spark bails out.

AO

Try unplugging the O2 sensor and see if it runs better. If it does, then you know (one of) the issue(s).

Tom. M

I think I will start with the ignition side first...coil swap, new wires, and see if that makes a diff...then it will be on to the fuel side..including O2, Maf etc..

AO

The LH reset (which results in better performance) is what leads me to think it;s the O2 sensor. My car does the exact opposite. If I disconnec teh LH, the car runs like crap for about 20 min. but slowly improves.

Tom. M

Very true, the battery disconnect will reset the brains to their stock settings programmed by the factory. As you drive, the brain "learns" the cars state of tune based upon the input of a variety of settings including o2, temp 1 and 2, etc etc. So, in my case it could likely be some sensor telling the brain to do something it obviously shouldn't. could be the O2..unplug is on the checklist...

In most cases, one should not experience much difference and an unplugged brain won't need to learn to make the car run properly (those that don't see degraded performance after brain disconnect). Those that are out of tune for one reason or another will see rough running until the brain compensates for the engines state of tune...

mark kibort

i heard the brain needs to be unplugged for a long time before it is reset. Ive done dyno runs with unplugging the brain, (cycling power) and it had little or no effect) BUT, overnight, things change. (from what was said from this discussion on another thread)

mk